1. Field of the Invention
The present invention generally relates to apparatus and methods useful in detecting, recording, analyzing and displaying phonocardiographic sounds. The present invention is particularly directed to a recording, digital stethoscope for detecting both phonocardiographic sounds and electrocardiographic wave patterns and for digitalizing and storing those signals. More particularly, the present invention further includes computer and display features for analyzing the digitalized signals to produce a characteristic phonocardiographic signature for the patient, for comparing that signature with stored reference signatures to select the most similar reference signatures and for displaying both audibly and visually the phonocardiographic sounds which produced one or more of the selected reference signatures and the signature produced for the patient.
2. Description of the Background
The heart and body produce hundreds of specific sounds, including heart, lung, bowel, circulatory and Korotkoff sounds. These sounds and combinations thereof are indicative of normal and abnormal conditions. Knowledge of these sounds provides valuable diagnostic information to the physician. The art of listening to these sounds and using them as diagnostic aids is known as auscultation. The ancients listened to these sounds by placing the ear to the chest or back of the patient. Later, the air column stethoscope was developed. The stethoscope has proven to be a valuable instrument for the transmission of these sounds to the examining physician. The air column stethoscope has remained relatively unchanged for more than a century. Recently, electronic stethoscopes using a transducer and appropriate electronics to detect the sounds have been developed.
The heart produces an electrical wave pattern and many complex sounds which can provide much valuable diagnostic information. However, the average physician typically has difficulty in interpretation of the highly complex sounds and combinations of sounds produced by the heart. Physicians especially trained to interpret these electrical patterns and sounds are known as cardiologists. Because a cardiologist often is not available, much of the information contained in these electrical patterns and sounds may be lost. Accordingly, it is desirable to provide an apparatus and method for recording these sounds to permit later analysis by a cardiologist. In an effort to address this problem, several recent patents have disclosed apparatus for recording the electrocardiographic wave patterns while others have disclosed apparatus for recording the phonocardiographic sounds. Even more desirable would be an apparatus and method which, in addition to such recording, would provide the average physician with assistance in making diagnoses based upon these sounds.
The standard air column stethoscope used by the medical profession employs a listening cup placed on the chest or back of the patient with the sound amplified by a simple bell and diaphragm into a standing air column terminating in earpieces for the physician's ears. The conventional stethoscope has remained relatively unchanged since the last century. Electronic stethoscopes have also been available for some time. In an electronic stethoscope the heart sounds are detected by a transducer and are electronically processed. The electronically processed signals are then employed to drive a speaker providing sound to an individual listener or to a group. Such devices permit amplification of the detected sounds. Recently recording capability, first analog and later digital, has been added to the electronic stethoscope. However, due to various problems, including excessive noise, electronic stethoscopes have not become popular.
Many problems exist with the use of conventional stethoscopes. In general, conventional stethoscopes offer very subjective information. For example, the hearing acuity of the user has significant bearing on the sounds observed. When a loud sound is followed by a soft sound, difficulty exists in detecting and assessing the intensity of the soft sound. This acoustical phenomenon is known as masking. It is difficult to time an abnormal heart sound with respect to the phase of the heart beat, an important aspect of murmur diagnosis. A fast heart rate can make both the recognition and timing of abnormal sounds difficult. This problem is often found with children and animals where heart rates are often much higher than in adult humans. External noise may often mask heart, lung, circulatory and Korotkoff sounds detected under non-ideal listening conditions. These and many other problems plague the conventional stethoscope.
Many of these subjective factors may be removed by visual display of the heart sounds. Most efforts at visual display of heart data have been directed to the electrocardiographic wave pattern. Because the electrocardiographic wave pattern, i.e., the electrical wave pattern generated by the heart, is more easily processed and displayed, the electronic monitoring, displaying and storing of the electrocardiographic wave pattern was addressed first. Many patents deal with the detection, storage and display of the electrocardiographic wave pattern.
Early efforts to visually display heart data were disclosed by Vogelman in U.S. Pat. No. 3,921,624. Bax in U.S. Pat. No. 4,331,159 disclosed the acquisition and visual display of analog electrocardiographic wave patterns on a helical track about a rotating cylinder. Shimoni in U.S. Pat. No. 4,617,938 and Citron in U.S. Pat. No. 4,417,306 disclosed systems for acquiring and recording electrocardiographic wave patterns. Both Bax and Shimoni disclosed the identification of the R-wave, that marker of the wave pattern separating the systolic and diastolic portions of the heart beat. Both Ascher in U.S. Pat. No. 4,596,256 and Lisiecki in U.S. Pat. No. 4,519,398 disclosed portable electrocardiographic wave recorders. Further, Lisiecki disclosed a transfer of the recorded signals to a fixed computer for visual display. Anderson in U.S. Pat. No. 4,628,327 disclosed the acquisition, digitalization and storage of electrocardiographic wave patterns in a circular memory. Upon tripping of an alarm indicating a preset abnormal condition, the attached recorder rapidly produces a visual output of the stored data both before and after the event which tripped the alarm. Yoneda in U.S. Pat. No. 4,779,199 similarly disclosed acquisition and digitalization of the electrocardiographic wave pattern. Further, U.S. Pat. No. 4,115,864 and U.S. Pat. No. R 29,921 both disclosed the acquisition and storage of electrocardiographic wave pattern data followed by a display of that data with previously recorded electrocardiographic wave patterns to permit a visual comparison of the results by the physician.
As the above patents illustrate, most efforts at electronic storage and display of heart data have been directed to the electrocardiographic wave pattern. This is because the ECG wave pattern is much simpler and at a significantly lower frequency than the phonocardiographic heart sounds. Detection, digitalization, storage and display of the phonocardiographic heart sounds are complicated by the presence of many other body sounds and by their higher frequency and more variable wave pattern. However, some work has been done in this area. Slavin in U.S. Pat. No. 4,483,346 disclosed a portable device for recording both an electrocardiographic wave pattern and phonocardiographic sounds. The phonocardiographic sounds were digitalized and stored for later transmission through a modem to a computer for storage and display. In U.S. Pat. No. 4,624,263, Slavin added cassette storage capability to the previously disclosed portable recorder. Further, Slavin disclosed the storage of abnormal phonocardiographic information for displaying with the patient's heart sounds to illustrate differences.
There has been a long felt but unfulfilled need within the medical profession for a device capable of aiding the non-specialist physician without access to a cardiologist for analyzing heart sounds. The present invention provides such an apparatus and method. Although the above patents disclose systems for detecting, storing and displaying the electrocardiographic wave pattern and, in the Slavin patents, the phonocardiographic heart sounds, none of these patents disclose a stethoscope capable of detecting and recording simultaneously both the phonocardiographic heart sounds and the electrocardiographic wave pattern while also providing a conventional air column listening device. None of the above patents discloses a system for analyzing the complex, phonocardiographic heart sounds to identify a plurality of characteristic features to produce a phonocardiographic signature for the patient. Further, none of the above patents discloses a system for comparing a patient's phonocardiographic signature with PCG signatures for a variety of normal and abnormal heart sounds maintained in a reference library to aid the physician in diagnosis. Finally, none of the above patents discloses a system for displaying one or more reference sounds selected after comparison of the phonocardiographic signatures.